1. Field of the Invention
The invention relates to a process and an apparatus for the production of an injection molded part, in particular an apertured information carrier disk.
2. Description of the Related Technology
The sprue funnel serves, by virtue of its specific configuration, to introduce liquified plastic material arriving from the channel of the injection molding nozzle into the molded cavity. The sprue funnel effects a uniform distribution around the circumference and diverts the plastic material by 90.degree.. The sprue part formed in the course of the injection molding process in the sprue cavity must be cut and removed from the molding after the cooling phase.
DE-OS No. 28 38 634 shows a device to cut the sprue part, which is integrally joined to the molding, by punching and ejecting the sprue by a sprue ejector in the production of an annular molding by an injection molding process. The two-part injection mold is opened by displacing both parts of the mold axially from each other to punch out the sprue part. The separation of the two mold parts is effected in two steps, i.e., initially only far enough so that the sprue part which is held in an undercut is punched into the free space created in this manner by a hydraulically actuated tubular ejector, wherein the sprue is still held by the undercut. Subsequently, the mold is opened completely and the sprue part pushed out of the undercut by an ejector pin guided in the tubular ejector, so that it drops downward in the parting plane of the injection molding tool.
Precision and freedom of dust requirements are extremely high in information carrier disks, such as sound and image carrier disks produced by an injection molding process. Particular problems arise in the creation of a center opening by the punching of the sprue part from the disk, as shown in DE-OS No. 28 38 634.
The tolerance limits of the fit diameter of the opening are larger than those of the other dimensions of the disk due to the punching process. The surface of the punched opening is also rougher than those of the rest of the injection molded surface of the disk. The dust particles necessarily produced in the process may affect the molded article. In the course of the production of information carrier disks dust may be deposited on the die plate used in the process, which would be embedded in the product in the next molding step.
A disk produced with embedded dust would exhibit impaired reproduction quality, possibly rendering the disk unusable. The punching process further generates stresses which may have a detrimental effect on the product.